[PATCH] variable size arrays in nested functions (take 2)

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Feb 09, 2001 at 03:17:59PM -0800, Richard Henderson wrote:
> On Fri, Feb 09, 2001 at 03:07:47PM -0500, Jakub Jelinek wrote:
> > Basically, what's going on is that variable_size takes care of putting the
> > SAVE_EXPR on pending list, but SAVE_EXPRs can be created deeply from fold
> > (the problematic SAVE_EXPR is actually created from within build_array_type
> > when building TREE_SIZE()). get_pending_sizes() takes care of fixing up
> > context of the SAVE_EXPRs recorded by variable_size but this one slips
> > through.
> 
> Oh.  I see.  Dear lord this is ugly.  Let us all look forward to that
> blessed day in which SAVE_EXPR is forever banished to the pit.
> 
> I have a feeling that the code in extract_muldiv that is creating the
> new SAVE_EXPR in question is not safe.  I think it _was_ safe when we
> were evaluating things a statement at a time, but not now that we are
> doing functions as trees.  Because now "SAVE_EXPR_RTL (t) == 0" doesn't
> mean that there isn't a (program order) previous ocurrence of T and
> a subsequent modification of one of T's arguments.
> 
> Does removing the SAVE_EXPR case from extract_muldiv also solve the
> problem?

Yes, on the other side I was afraid if it would not create any code
generation regressions.
Would a patch like below be ok as well (basically if save_expr is on the
pending list, add the new one there as well)?

2001-02-13  Jakub Jelinek  <jakub@redhat.com>

	* stor-layout.c (is_pending_size, put_pending_size): New functions.
	(variable_size): Call put_pending_size.
	* tree.h (is_pending_size, put_pending_size): Add prototypes.
	* fold-const.c (extract_muldiv): If SAVE_EXPR is on the pending
	sizes list, put newly created SAVE_EXPR there as well.

	* gcc.c-torture/execute/20010209-1.c: New test.

--- gcc/stor-layout.c.jj	Fri Feb  9 01:35:10 2001
+++ gcc/stor-layout.c	Tue Feb 13 20:02:32 2001
@@ -80,6 +80,30 @@ get_pending_sizes ()
   return chain;
 }
 
+/* Return non-zero if EXPR is present on the pending sizes list.  */
+
+int
+is_pending_size (expr)
+     tree expr;
+{
+  tree t;
+
+  for (t = pending_sizes; t; t = TREE_CHAIN (t))
+    if (TREE_VALUE (t) == expr)
+      return 1;
+  return 0;
+}
+
+/* Add EXPR to the pending sizes list.  */
+
+void
+put_pending_size (expr)
+     tree expr;
+{
+  if (TREE_CODE (expr) == SAVE_EXPR)
+    pending_sizes = tree_cons (NULL_TREE, expr, pending_sizes);
+}
+
 /* Put a chain of objects into the pending sizes list, which must be
    empty.  */
 
@@ -140,7 +164,7 @@ variable_size (size)
        that determine sizes for variable size objects.  */
     ;
   else
-    pending_sizes = tree_cons (NULL_TREE, size, pending_sizes);
+    put_pending_size (size);
 
   return size;
 }
--- gcc/tree.h.jj	Fri Feb  9 01:35:07 2001
+++ gcc/tree.h	Tue Feb 13 19:34:13 2001
@@ -2127,6 +2127,8 @@ extern tree size_int_type_wide		PARAMS (
 extern tree round_up			PARAMS ((tree, int));
 extern tree round_down			PARAMS ((tree, int));
 extern tree get_pending_sizes		PARAMS ((void));
+extern int is_pending_size		PARAMS ((tree));
+extern void put_pending_size		PARAMS ((tree));
 extern void put_pending_sizes		PARAMS ((tree));
 
 /* Type for sizes of data-type.  */
--- gcc/fold-const.c.jj	Fri Feb  9 01:35:08 2001
+++ gcc/fold-const.c	Tue Feb 13 19:55:42 2001
@@ -4454,7 +4454,14 @@ extract_muldiv (t, c, code, wide_type)
       if (SAVE_EXPR_RTL (t) == 0 && ! TREE_SIDE_EFFECTS (TREE_OPERAND (t, 0))
 	  && 0 != (t1 = extract_muldiv (TREE_OPERAND (t, 0), c, code,
 					wide_type)))
-	return save_expr (t1);
+	{
+	  t1 = save_expr (t1);
+	  if (SAVE_EXPR_PERSISTENT_P (t) && TREE_CODE (t1) == SAVE_EXPR)
+	    SAVE_EXPR_PERSISTENT_P (t1) = 1;
+	  if (is_pending_size (t))
+	    put_pending_size (t1);
+	  return t1;
+	}
       break;
 
     case LSHIFT_EXPR:  case RSHIFT_EXPR:
--- gcc/testsuite/gcc.c-torture/execute/20010209-1.c.jj	Fri Feb  9 01:13:27 2001
+++ gcc/testsuite/gcc.c-torture/execute/20010209-1.c	Fri Feb  9 01:13:18 2001
@@ -0,0 +1,21 @@
+int b;
+int foo (void)
+{
+  int x[b];
+  int bar (int t[b])
+  {
+    int i;
+    for (i = 0; i < b; i++)
+      t[i] = i + (i > 0 ? t[i-1] : 0);
+    return t[b-1];
+  }
+  return bar (x);
+}
+
+int main ()
+{
+  b = 6;
+  if (foo () != 15)
+    abort ();
+  exit (0);
+}

	Jakub